Carbon-based metal composite material, method for preparation thereof and use thereof

ABSTRACT

According to the present invention, there is provided a carbon-based metal composite material comprising a carbonaceous matrix and a metal component dispersed in said carbonaceous matrix, wherein at least 90 volume percent of the pores of the carbonaceous matrix is substituted with said metal component, and the content of said metal component is 35% or less based on the total volume of said carbon-based metal composite material; a method of producing a carbon-based metal composite material wherein impregnation of the carbon formed body with molten metal under pressure is carried out by pre-heating said carbon formed body and then impregnating the open pores of the carbon formed body with molten metal under a pressure of at least 200 kg/cm 2  of the cross-sectional area of the plunger; and a substrate-shaped formed body for an electronic component comprising a carbon-based metal composite material.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP99/06304 which has an Internationalfiling date of Nov. 11, 1999, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a novel carbon-based metal compositematerial, a method for its production and various applications usingsaid carbon-based metal composite material. In more detail, it relatesto a carbon-based metal composite material comprising a carbonaceousmatrix and metal components dispersed in said carbonaceous matrix, amethod of impregnating a carbon material with metal components, and usesof a carbon-based metal composite material, such as high thermalconductivity-low, thermal expansivity substrates for packagingsemi-conductors, astronautical components or general industrialstructural materials having excellent specific strength and specificrigidity, heat resistant materials such as for gas turbines, andelectrical contact materials having excellent sliding characteristics.

BACKGROUND OF THE INVENTION

Conventional metal composite materials containing carbon materials areproduced by dispersing and orientating carbon particles or carbonfibers, as reinforcing materials, in a metal component matrix.Furthermore, there have been adopted production methods according to theso-called powder metallurgy method using graphite powder and metalpowder as starting materials.

These types of metal-carbon composite materials each use carbonmaterials to try to improve the characteristics of the metal component,as the parent material for the composite material, and should be calledmetal-based carbon composite materials having a metal component as theparent material. Such materials having a much larger volume of carbonthan metal component have not been realised, and these materials aretherefore themselves limited in their performance.

On the other hand, carbon materials have been widely used as result oftheir excellent heat resistance and workability. However, they have manypoints that need to be improved such as being brittle, having lowstrength, being easily damaged, having low oxidation resistance, beingdifficult to plate, and having low heat conductivity. One reason forthis is that, with the exception of special carbon materials, carbonmaterials generally have pores, as a result of which the electrical,heat and chemical properties naturally possessed by carbon are not fullyexhibited.

It has been attempted to improve the characteristics of carbon materialsby filling the pores of the carbon material with metal material therebyforming a carbon-metal composite. For example, a material having some ofthe pores substituted with molten copper, copper alloy or silver hasbeen proposed in order to improve the electrical characteristics ofcarbon materials. However, it was impossible to obtain a material havinga large portion of the pores substituted with metal, and its performancewas not sufficient.

In general, carbon materials and molten metals have poor wettability,and it was almost impossible in previous studies to impregnate the poresof carbon materials with molten metal components. Although thewettability was improved at high temperatures, casting impregnation athigh temperatures resulted in a reaction between the carbon componentand the metal component. This resulted in a deterioration in the carbonmaterial, with the problem that it was impossible to obtain thecharacteristics of a metal-based carbon composite material.

In other words, the production of a composite by the impregnation of acarbon material with metal components by a production method accordingto the conventionally proposed conditions and operations results in areaction at the interface between the carbon component and the metalcomponent and the generation of the metal carbide. This had, forexample, the ill effect of these two components peeling away from eachother, and a carbon-based metal composite material having excellentstrength and other properties had not been developed.

Along with the technical development of this type of metal-carboncomposite materials, there has been an increase in the amount of heatgenerated by electronic devices as a consequence of their improvedperformance and capacity, and there has been a focus on carbon-basedmetal composite materials having a high proportion of carbon componentand having excellent strength as a high thermal conductivity-low thermalexpansivity material effective for heat removal. The development ofthese materials is now eagerly anticipated.

DISCLOSURE OF THE INVENTION

A first objective of the present invention is, in light of theabove-mentioned problems with the techniques developed to date, toprovide a carbon-based metal composite material which maintains a highdegree of heat resistance and high thermal conductivity as well ashaving a controlled thermal expansivity and excellent strength.

A second objective of the present invention is to provide a method ofproducing a carbon-based metal composite material comprisingimpregnating a molten metal into the pores of a carbon formed bodywhilst inhibiting reactions between carbon and the metal:

Furthermore, a third objective of the present invention is to provide amaterial for an electronic component having a high thermal conductivityand a controlled thermal expansivity useful for the removal of heat froman electronic component.

A fourth objective of the present invention is to provide a carbon-basedmetal composite material provided with an insulator film.

The inventors of the present invention have found, as result ofextensive research into achieving the above-described objectives, that ahigh thermal conductivity-low thermal expansivity composite material canbe obtained by impregnating the pores of a carbon material with a metalcomponent under molten and pressurized conditions, and that theabove-described objectives can be achieved using the same. It was on thebasis of these findings that the present invention was completed.

In other words, the present invention firstly relates to a carbon-basedmetal composite material comprising a carbonaceous matrix and a metalcomponent dispersed in said carbonaceous matrix characterised in that

(1) at least 90 volume percent of the pores of said carbonaceous matrixare substituted with said metal component, and

(2) the content of said metal component is 35% or less based on thetotal volume of said carbon-based metal composite material.

Furthermore, the present invention secondly relates to a method ofproducing a carbon-based metal composite material comprisingimpregnating a carbon formed body with a molten metal by contacting saidcarbon formed body with said molten metal under pressure, characterisedin that

(1) said carbon formed body is pre-heated to a temperature at or abovethe melting point of said molten metal under an inert gas atmosphere;and

(2) said pre-heated carbon formed body is impregnated with said moltenmetal under a pressure of at least 200kg per cm² of the cross-sectionalarea of the plunger.

Furthermore, the present invention thirdly relates to a substrate-shapedformed body for an electronic component characterised in that it isformed from a carbonaceous metal composite material comprising acarbonaceous matrix and a metal component dispersed in said carbonaceousmatrix, wherein at least 90 volume percent of the pores of saidcarbonaceous matrix are substituted with said metal component, and thecontent of said metal component is 35% or less based on the total volumeof said carbonaceous metal composite material.

Furthermore, the present invention fourthly relates to a carbon-basedmetal composite material provided with an insulator film obtained bycovering the surface of a carbonaceous metal composite material with aninsulator material, the carbonaceous metal composite material having acarbonaceous matrix and a metal component dispersed in said carbonaceousmatrix, wherein at least 90 volume percent of the pores of saidcarbonaceous matrix are substituted with said metal component, and thecontent of said metal component is 35% or less based on the total volumeof said carbonaceous metal composite material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the basic construction of productionapparatus used in the method of producing the carbon-based metalcomposite material of the present invention.

FIG. 2 is a conceptual view of a 2D carbon composite material used inExample 4.

FIG. 3 is a cross-sectional view of an electronic component showing anexample of a use of a carbon-based metal composite material substrate ofthe present invention.

FIGS. 4-1 and 4-2 are plane and elevated views of a cooling componentproduced in Example 7 having a substrate on both sides.

FIGS. 5-1 and 5-2 are side and plane views of a cooling componentproduced in Example 8 having cooling fins on one side.

FIG. 6 is a cross-sectional view of an electronic component showing ause of a carbon-based metal composite material provided with an aluminafilm produced in Example 9.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

The carbon-based metal composite material of the present inventioncomprises a carbonaceous matrix and a metal component dispersed in saidcarbonaceous matrix, wherein the metal component fills at least 90volume percent of the pores of the carbonaceous matrix, and has acontent of 35% or less based on the total volume of the carbon-basedmetal composite material.

Furthermore, one characteristic of the method of producing acarbon-based metal composite material of the present invention is thatit comprises a step (1) of pre-heating a carbon formed body and a step(2) of pressurized impregnation of molten metal.

CARBONACEOUS MATRIX

The carbonaceous matrix which composes the carbon-based metal compositematerial of the present invention is a carbon material which can form acomposite together with a metal component. Examples of carbon materialswhich can be used for the carbonaceous matrix include (a) general carbonmaterials produced with normally employed starting materials andmethods; (b) carbon fiber-reinforced carbon composite materials obtainedby forming a composite from carbon fibres and a carbon-containingcompound; and (c) a pressure-formed body comprising carbon powder,artificial graphite powder or carbon fibers. Graphite-type carboncrystals, namely, carbon materials having specific pore structure suchas pore diameter and pore volume are preferred. In this specification,these carbon materials prior to formation of a composite with the metalshall, where necessary, be referred to as a “carbon formed body”. Theshape of the carbon formed body can be freely selected according to theshape required in the use of the carbon-based metal composite material.

(a) General Carbon Materials

The carbon materials used as the carbonaceous matrix of the carbon-basedmetal composite materials of the present invention may be onescomprising amorphous carbon or graphite-type crystals, or mixtures ofthese. However, ones comprising graphite-type crystals are excellent interms of uniformity of pore characteristics and are particularlypreferred from the viewpoint of inhibiting the reactions with the metalcomponent. It is important to select a graphite-type crystal having anaverage interplanar spacing d measured by X-ray diffraction of 0.340 nmor less.

Examples of carbon formed bodies for use as the carbonaceous matrixinclude ones having a porosity prior to impregnation with the metalcomponent of less than 40 volume percent, preferably, 2 to 35 volumepercent, and further preferably, 5 to 25 volume percent. Namely, oneswherein the volume percentage of the carbonaceous part is at least 60volume percent, preferably at least 75 volume percent.

If the porosity were to exceed 40 volume percent, there is the concernthat the metal component content may increase excessively making itdifficult to provide both the required thermal conductivity and thermalexpansivity. The pore diameter of the carbon material is not limited andmay be distributed over a wide range stretching from submicrometers toseveral hundred microns. Examples of carbon materials include oneshaving an average diameter of, preferably 0.1 μm to 10 μm, furtherpreferably, 0.1 μm to 3 μm. When the average pore diameter is thuswithin a specific range, the impregnation of the metal component isfacilitated according to specific production conditions making itpossible to increase the filling percentage to 90 volume percent ormore, and furthermore to 95 volume percent or more, therebysubstantially achieving a filling percentage of 100 volume percent. Thefilling percentage refers to the volume proportion occupied by metalimpregnated into the pores.

Furthermore, it is preferred that the density of the carbon formed bodyprior to impregnation of the metal component is in the range of 1.4g/cm³ to 2 g/cm³, preferably 16 g/cm³ to 2 g/cm³, and particularly 1.7g/cm³ to 1.9 g/cm³. If the density is less than 1.4 g/cm³, there is theill effect of the the thermal expansivity becoming excessively large dueto a high metal percentage. On the other hand, if the density exceeds 2g/cm³, the metal impregnation-filling percentage is reduced. There isthe problem that even if almost all the pores could be filled, the metalpercentage would be small whereby a thermal expansivity useful for asubstrate for an electronic component (4×10⁻⁶/° C. or more) cannot beachieved.

Specific examples of carbon materials for use as the carbonaceous matrixinclude those of electrodes used in electrolytic furnaces for electricfurnace steel production, aluminium refining etc., electrodes forelectric discharge machining, tools for producing silicon semiconductorsor optical fibers, and carbon formed bodies used as heat resistantstructural materials.

These kind of carbon materials can be produced via the main steps ofmixing, forming, calcination and graphitisation etc. using a filler andbinder as starting materials. Calcined oil coke, calcined pitch coke,natural graphite, calcined anthracite, carbon black etc. can be freelyused as the filler, and coal tar pitch, coal tar, and synthetic resinsetc. can be freely used as the binder. The operation and conditions foreach of the mixing, forming, calcination and graphitisation steps may beas those employed conventionally, and can be appropriately determined togive the above-mentioned desired shape and properties. Theabove-mentioned graphite-type crystals can be obtained by calcinationtreatment in an inert gas at a temperature of 2500° C. or more,particularly, 2800° C. or more.

Extrusion, moulding and cold isostactic pressing (CIP method) can berecited as examples of methods of forming the carbon formed body.Extrusion and moulding are particularly preferred.

(b) Carbon Fiber-reinforced Carbon Composite Materials

Carbon fiber-reinforced carbon composite materials are carbon/carboncomposite materials (referred to hereunder as “c/c composite materials”where necessary) constructed from carbon fibers and carbon-containingcompounds. The carbon fibers are used as filler. There are providedone-dimensional, two dimensional, and three-dimensional forms ofcomposite materials according to the manner of orientation of thefibers, starting with composite materials using fibers orientated in onedirection (1D), and moving from flat arranged fibers (2D) to compositematerials using 3D wovens. The type of material can be freely selectedaccording to the use.

The c/c composite material used as the carbonaceous matrix of thecarbon-based metal composite material of the present invention may alsobe one made from amorphous carbon, but one in which the carbon fibers orthe carbon matrix or both comprise graphite-type crystals is preferred.Furthermore, in terms of density, one having a density of 1.6 g/cm³ to 2g/cm, preferably, 1.7 g/cm³ to 1.9 g/cm³ may be used.

The pore structure of the c/c composite material may be the same as thatof the afore-mentioned general carbon materials. The average porediameter is in the range of 0.5 μm to 5 μm, preferably 1 μm to 2 μm. Itis preferred to have a porosity of 5% to 30%, preferably 10% to 25%.

As mentioned above, the c/c composite material may be produced by anymethod. It may be produced by impregnating a carbon matrix precursorsuch as a phenol resin or oil pitch between the carbon fibers, followedby forming and calcination in an inert gas, normally at a temperature of1000° C. or greater. If the calcination temperature is controlled to be2500° C. or greater, particularly, 2800° C. or greater, a graphitisedcrystal-containing carbon material can be obtained.

Furthermore, as a method of avoiding the re-impregnation of the matrixprecursor required in conventional methods, a method comprisingimpregnating carbon fibers at a heat treatment temperature of 500° C. orhigher with a liquid having dispersed therein carbon powder containingat least 50 weight percent of raw coke powder followed by volatising thesolvent and shaping and calcinating the carbonaceous matrixprecursor-containing carbon fibers under pressure (reference is made toJapanese Patent Application Laid-Open No.247563/1991) may be employedwhereby a carbon material having properties favourable for thecarbonaceous matrix of the carbon-based metal composite material of thepresent invention can be obtained.

A specific example of a carbon fiber-reinforced carbon compositematerial is shown in FIG. 2. In the figure, the fibers are orientated ina unilateral direction, and the respective layers are stacked with thefiber direction at 0° and 90°. Length is indicated by the xy direction,and depth by the z direction.

(c) An example of a pressure-formed body comprised of carbonpowder/artificial graphite or carbon fibers is a carbon composite bodyobtained by filling an iron vessel with graphite powder, carbon fibersetc. and applying pressure. It has a porosity controlled to be between10 and 30 volume percent, and is useful as a starting material for thecarbonaceous matrix of the present invention. Specific examples ofcarbon formed bodies are ones containing at least 10 percent on a volumebasis of graphite particles having a length between 1.0 mm and 3 mm, orones containing at least 10 percent on a volume basis of pitch carbonfibers having a fiber length of 0.02 mm to 5 mm, or ones containing atleast 10 percent on a volume basis of graphite particles having a lengthof 0 mm to 3 mm and pitch carbon fibers having a fiber length of 0.02 mmto 5 mm. These carbon formed bodies are particularly useful as thecarbonaceous matrix for the substrate-shaped formed body for anelectronic component discussed hereafter.

METAL COMPONENT

The metal component composing the carbonaceous metal composite materialof the present invention may be freely selected according to the use.Examples include magnesium, aluminium, titanium, iron, cobalt, nickel,copper, zinc, silver, tin and alloys of each metal.

Preferred metal components include aluminium, copper, silver and alloysof these metals. Pure metal components of aluminium or copper areparticularly preferred. These metal components are favourable forproviding the specific thermal conductivity and thermal expansivityconsidered to be one of the characteristics of the carbonaceous metalcomposite material of the present invention.

CARBON-BASED METAL COMPOSITE MATERIAL

The carbon-based metal composite material of the present inventioncomprises the above-described carbonaceous matrix and a metal componentdispersed in said carbonaceous matrix, wherein 1) at least 90 volumepercent of the pores of the carbonaceous matrix are filled with themetal component; and 2) the content thereof is 35 percent or less basedon the total volume of the carbonaceous metal composite material.

It is preferred that the above-described metal component fills the poresof the carbonaceous matrix such that it occupies at least 90 volumepercent, particularly 95 volume percent of all open pores. It is furtherpreferred that substantially 100 volume percent of the pores are filled.If the filling percentage is less than 90 volume percent, the requiredproperties such as thermal conductivity cannot be satisfied. With theconventionally proposed methods of impregnating molten metal, a value of70 volume percent was achieved at best; there was no disclosure of amaterial having a high filling percentage. The carbonaceous matrix isamorphous carbon, graphite-type crystalline carbon and a mixture ofthese. Graphite-type carbon is particularly preferred. The form in whichthe metal component exists in the carbonaceous matrix can be observedusing a scanning electron microscope.

Next, the content of the metal component in the carbon-based metalcomposite material of the present invention is 35 volume percent orless, preferably 30 volume percent or less, and further preferably,between 5 and 25 volume percent. If the content exceeds 35 volumepercent, it becomes difficult to achieve a low thermal expansivity eventhough a high thermal conductivity may be achieved.

The density of the above-described carbon-based metal composite materialof the present invention will vary depending on the type of metalcomponent, but when aluminium is used as the impregnant, the density isin the range of 2 g/cm³ to 2.4 g/cm³, preferably 2.1 g/cm³ to 2.2 g/cm³,whereby a material having a thermal conductivity of 200 W/(m·K) or more,and a coefficient of a thermal expansion of 12×10⁻⁶/° C. or less,particularly from 4×10⁻⁶/° C. to 12×10⁻⁶/° C. can be provided.

There are no particular limitations with respect to the shape of thecarbon-based metal composite of the present invention. It can be formedinto various shapes at the stage of production depending on the use. Forexample, it may be formed into plates, blocks, sheets, films, granules,powder, fibers and woven fibers, non-woven fibers and shaped parts suchas arbitrarily machined parts.

METHOD OF PRODUCING THE CARBON-BASED METAL COMPOSITE MATERIAL

Next, a method of producing the carbon-based metal composite material ofthe present invention shall be described. According to the presentinvention, there is provided a method of producing a carbon-based metalcomposite material comprising the pressurised impregnation of a carbonformed body with molten metal by contacting the carbon formed body withthe molten metal under pressure, the method including the followingsteps (1) and (2).

(1) step of pre-heating the carbon formed body in an inert gasatmosphere at a temperature at least as high as the melting point of themolten metal; and

(2) step of impregnating the pre-heated carbon formed body with saidmolten metal at a pressure of 200 kg per cm² of the cross-sectional areaof the plunger.

Any carbon material suitable for the above-described carbonaceous matrixcan be used as the carbon formed body. A specific example of a carbonformed body is one having a density of 1.4 g/cm³ to 2 g/cm³, and aporosity of 50% or less, preferably, 35% or less, and furtherpreferably, 5% to 25%.

Specifically, in the above-described step (1), the carbon formed body isplaced into a mold and pre-heated in an inert gas atmosphere. Argon gas,nitrogen gas etc. may be used as the inert gas atmosphere. In thepre-heating, the temperature is maintained at or above, particularly atleast 100° C. above, and preferably of 100° C. to 250° C. above themelting point of the metal component. By proceeding via this step (1),the pores of the carbon material can be sufficiently impregnated withthe metal whilst inhibiting reactions at the interface between carbonand the metal.

Next, in step (2), the metal component is preferably heated to atemperature from 50° C. to 250° C. higher than the melting point of themetal component and supplied to the mold to contact it with theabove-mentioned pre-heated carbon formed body. A pressure of at least200 kg per cm² of the cross-sectional area of the plunger is applied toimpregnate the above-mentioned carbon formed body with the molten metal.In the case that aluminium is used in step (2), increasing thetemperature of the molten metal to more than 200° C. above the meltingpoint results in a tendency for deliquescent aluminium carbide to beformed whereby a practical composite material cannot be obtained.Furthermore, if the pressure is less than 200kg/cm², the impregnation ofthe metal cannot be carried out efficiently with a resulting decrease inthe filling percentage.

The impregnation of the molten metal in the method of producing thecarbon-based metal composite material of the present invention ischaracterised by the use of the plunger for a squeeze casting of apressure applicator of a standard press to inject the molten metal intothe carbon formed body placed inside the mold and directly applypressure thereto. It is thereby possible to obtain a composite materialhaving a high filling percentage which was not possible with theconventional gas pressure methods carried out in the presence of a gasinside a pressure-resistant vessel. It is also possible to obtain alarge scale composite material which was not possible with the priorart.

After the completion of step (2), a carbon-based metal compositematerial can be obtained via steps such as cutting etc.

In the case of a metal having a high melting point, the impregnation ofthe metal component can also be carried out by forming holes in thecarbon formed body and injecting the molten metal into the holes.

A specific example of apparatus used in the method of producing acarbon-based metal composite material according to the present inventionis shown in FIG. 1.

In FIG. 1, 11 is a metal mold, 12 is a plunger and 13 is a press. Acarbon formed body 4 is placed inside the mold 11, and is thenpre-heated in argon gas according to the above-described step (1).Molten metal heated to a specific temperature is then supplied, andplunger 12 is used to apply pressure to the molten metal inside themetal mold and maintain these same conditions for a specified period oftime. After the elapse of the specific period of time, the whole mass ofmetal is removed from the mold and cut to obtain a metal-impregnatedcarbon-based composite material.

SUBSTRATE-SHAPED FORMED BODY FOR AN ELECTRONIC COMPONENT

Next, (1) a substrate-shaped formed body useful as a heat disperser foran electronic component, and (2) a substrate-shaped formed body providedwith a cooling device shall be described as uses of the carbon-basedmetal composite material of the present invention.

In electronic components which are provided with an electronic circuitsupporting substrate for an electronic circuit comprising semiconductorelements, resistors, transformers, condensors and wiring and with a basesubstrate for supporting the electronic circuit supporting substrate;most of the heat generated by the electronic circuit is transferred fromthe electronic circuit supporting substrate and base substrate to acooling device and is finally released to the atmosphere or to a coolingliquid. Conventionally, aluminium, copper or alloys of these were usedas the base substrate material, but there is a problem of warping andpeeling as a result of a difference in thermal expansivity with theelectronic circuit.

The carbon-based metal composite material of the present invention has athermal conductivity of at least 150 W/(m·K) and a thermal expansivityin the range of 4×10⁻⁶/° C. to 12×10⁻⁶/° C.; it has improved substratecharacteristics compared to the above-described metal base substratesthus solving the above-discussed problems.

The substrate-shaped carbon formed body for electronic componentsaccording to the present invention preferably has a density of at least2 g/cm³. Specifically, in the case of aluminium- or aluminiumalloy-impregnated substrate-shaped carbon formed bodies, a density of 2g/cm³ to 2.4 g/cm³ is suitable, whereas in the case of a copper- orcopper alloy-impregnated substrate-shaped carbon formed body, a densityin the range of 2.3 g/cm³ to 4.6 g/cm³ is suitable.

A specific example of an electronic component including asubstrate-shaped carbon formed body comprising a carbon-based metalcomposite material according to the present invention and used as a heatdisperser for an electronic circuit is shown in FIG. 3.

In the figure, a substrate 30 comprising the carbon-based metalcomposite material of the present invention is joined to a ceramicinsulating substrate 32 via an adhesive layer 31. Synthetic resin,solder, metal brazing material etc. is used for the adhesive layer. Acircuit, circuit elements and parts 33 are provided on the ceramicinsulating substrate 32. A large amount of heat is generated from thecircuit, circuit elements and parts which is transferred to thesubstrate 30 and relased to a cooling device (not shown in the figure)joined to the bottom of the substrate 30.

Next, a substrate-shaped formed body provided with a cooling device foran electronic component shall be described as a use of the carbon-basedmetal composite material of the present invention.

The substrate-shaped formed body provided with a cooling device isobtained by simultaneously casting a carbon formed body and coolingdevice into an integrated body via the metal component at the time ofimpregnating the carbon formed body with the metal component. Thecooling device is made up of passages such as pipes for passing a liquidor fins for gas cooling. Specific examples of substrate-shaped formedbodies provided with cooling devices are shown in FIGS. 4-1 to 5-2.FIGS. 4-1 and 4-2 show a plane view and elevation view of a cooling parthaving a substrate-shaped formed body on both sides. Twosubstrate-shaped formed bodies 40 are prepared, and a semi-circulargroove A is cut into each of the formed bodies. A pipe 41 is fitted intothe groove, and then the two bodies are provisionally fastened together.The substrate-shaped bodies and the cooling device are integratedtogether by filling the space between the formed bodies and the pipewith molten metal at the same time as impregnating the pores with moltenmetal. In this way, the cooling performance can be improved.

FIGS. 5-1 and 5-2 show another embodiment consisting of a substrate foran electronic component having fins 51 joined to the bottom of asubstrate-shaped formed body 50. The surface of a metal mold 52 iscoated with a mold-release material made of carbon or BN powder, andthen the carbon formed body 50 and thin plates 51 are placed in themold. The thin plates 51 are metal plates having a melting point higherthan the carbon formed body or the metal to be impregnated, and form thefin blades. They are fitted into grooves provided in the carbon-formedbody. The top of FIG. 5-1 is a front view showing the electroniccomponent substrate having the fins 51 joined to the carbon formed body50 and placed in the metal mold 52 ready for impregnation with moltenmetal; FIG. 5-2 is a plane view thereof.

CARBON-BASED METAL COMPOSITE MATERIAL PROVIDED WITH AN INSULATING FILM

As another use of the carbon-based metal composite material of thepresent invention, there can be provided the same with its surfacecovered with an insulating material. Examples of insulating materialsinclude plastic materials such as polyimide resins,polyaminobismaleimides, bismaleimides, polyetheramides, polyamideimides,epoxys, polyurethanes, polyesters and ceramic materials such as alumina,aluminium nitride, silica, silicon nitride, titanium oxide, zirconia andglasses. The thickness of the covering layer of insulating material is0.6 mm or less, preferably 0.1 mm to 0.1 mm. There are no limitationsregarding the method of forming the covering layer, and any method maybe used. It is preferably formed by a sputtering method, coating method,CVD method, solgel method etc.

The carbon-based metal composite material of the present invention has aYoung's modulus of 30 GPa or less, a thermal conductivity of 100W/(m·K)or more, and a thermal expansivity of 12×10⁻⁶/° C. or less. Aninsulator-covered carbon-based metal composite material obtained usingthis can be used as an electronic device with a circuit laid directly onthe insulating film. This application example is shown in FIG. 6. InFIG. 6, the carbon-based metal composite material of the presentinvention is used as a substrate and an insulating film 62 is providedthereon via a joining layer 61; an electronic circuit may be providedthereon. In the figure, 64 is an electronic component such as asemiconductor element, a resistor or a condenser.

To describe it in more detail, the carbon-based metal composite materialof the present invention has a similarly low thermal expansivity and aYoung's modulus one order lower compared to a composite materialsubstrate produced by impregnating a powder sintered body of siliconcarbide, alumina, tungsten etc. with metal; and the top thereof can thusbe covered with a ceramics electrically insulating film having good filmproperties and resistant to heat cycles. An electronic circuit can beprovided on top of this insulating film, whereby an electronic componenthaving excellent thermal conductivity can be produced.

EFFECT OF THE INVENTION

The carbon-based metal composite material of the present invention has,by virtue of the above-described construction, at least 90 volumepercent, particularly 95 volume percent up to 100 volume percent of thepores of the carbonaceous matrix filled with the metal component.Furthermore, the metal component content is controlled to be no morethan 35% based on the total volume of the carbon-based metal compositematerial. By virtue of this composition, the carbon-based metalcomposite material of the present invention has a high thermalconductivity/low thermal expansivity characteristic, and can be providedas a substrate-shaped carbon formed body for an electronic component.Furthermore, in this type of carbon-based metal composite material, thepores can be impregnated with the molten metal at a high fillingpercentage by carrying out the impregnation of the pores of the carbonformed body with the molten metal instantaneously at high pressure;furthermore, in the case of aluminium impregnation, it is realised byinhibiting reactions between aluminium and carbon which was not possiblewith conventional techniques.

EXAMPLES

Hereunder, the present invention shall be specifically described byExamples and Comparative Examples. The present invention is, however,not to be limited in any way by these Examples etc.

Measurement methods and test methods were used for the evaluation of thequality and performance of the carbon-based metal composite materialsprepared according to the Examples and Comparative Examples.

1) Impregnation of the Metal Component

The state of dispersion of the metal component was observed at amagnification ratio of ×500 using a scanning electron microscope S2300made by Hitachi Ltd.

2) Porosity

The porosity of the carbon formed body prior to impregnation with themetal component is a calculated value calculated assuming the carbondensity to be 2.1 g/cm³ from its apparent density.

3) Metal Filling Percentage

[(Porosity prior to metal filling−porosity after metal filling)/porosityprior to metal filling)]×100

4) Specific Heat

Measured at room temperature in a flow of dry nitrogen at a temperaturerise of 10° C./min. according to the DSC method (DSC: differentialscanning calorimeter) using a DSC-2 made by the Perkin Elmer company.Sapphire was used for the comparative calibration.

5) Density

Measured according to the Archimedes method using an electronic analysisbalance AEL-200 made by Shimadzu Corporation.

6) Bending Strength

The bending strength of a prepared strength test piece was measuredusing a precision universal testing machine AG-500 made by ShimadzuCorporation. It was measured under the following conditions: test piecesize 4 mm×4 mm×8 mm; span distance 60 mm; crosshead lowering speed 0.5mm/min.

7) Thermal Conductivity

The thermal conductivity was determined as the multiple of the thermaldiffusivity, specific heat and density. The thermal diffusivity wasmeasured at 25° C. according to the laser flash method using a TC-7000made by Shinku Riko Kabushiki Kaisha. Ruby laser light (excitationvoltage:2.5 kV; 1 homogenising filter and 1 attenuation filter) was usedfor the irradiation.

8) Thermal Expansivity (Coefficient of Thermal Expansion)

The thermal expansivity from room temperature to 300° C. was measuredusing thermal analysis device 001, TD-5030 made by the Max Sciencecompany.

Example 1

Commerically available artificial graphite I (density: 1.85 g/cm³,porosity: 12%, bending strength: 3.5kg/cm³, thermal conductivity: 100W/(m·K), thermal expansivity: 3.8×10⁻⁶/° C.) was cut into a block havinga length of 30 mm, a width of 30 mm and a depth of 10 mm. The block wasplaced in an iron mold and heated in argon gas to 750° C. for 90minutes. Next, molten aluminium obtained by heating pure aluminiumgranules to 750° C. was added into the mold, and a pressure of 500kg percm² of the cross-sectional area of the plunger(the ram) was applied.This state was maintained for 30 minutes to impregnate the pores of theartificial graphite with aluminium and form the composite. Aftercooling, the whole mass of aluminium was removed and cut to obtain acarbon-based aluminium composite material having an aluminium content of12 volume percent.

The nature of the impregnation of the aluminium in the thus obtainedcarbon-based aluminium composite material was observed by theabove-described method. It could be confirmed that the pores had been100% substituted by the aluminium, and that the aluminium was disperseduniformly in the carbonaceous matrix.

A strength test piece was prepared and subjected to a bending test. Theresult was a bending strength of 8 kg/mm². The results are shown inTable 1. It can be seen from this that the bending strength hadincreased to twice the bending strength (4 kg/mm²) of the artificialgraphite I not impregnated with aluminium.

Furthermore, the thermal conductivity and the thermal expansivity wererespectively measured by the above-described methods. These results areshown in Table 1. The thermal conductivity had increased to 200 W/(m·K),which is twice that of the artificial graphite I (100 W/(m·K), and thethermal expansivity had risen from 3.8×10⁻⁶/° C. to 10.8×10⁻⁶/° C.

Example 2

Commerically available artificial graphite I was cut into a block havinga length of 30 mm, a width of 30 mm and a depth of 10 mm. The block wasplaced into a carbon mold and heated in argon gas to 1200° C. for 120minutes. Next, molten copper obtained by heating pure copper granules to1200° C. was added into the mold, and a pressure of 1000 kg per cm² ofthe cross-sectional area of the ram was applied. This state wasmaintained for 30 minutes to impregnate the pores of the artificialgraphite with copper and form the composite. After cooling, the wholemass of copper was removed and cut to obtain a carbon-based coppercomposite material having a copper content of 14 volume percent.

The nature of the copper impregnation in the thus obtained carbon-basedcopper composite material was observed by the above-described method. Nopores were observed, and it could be confirmed that the copper wasdispersed uniformly in the carbonaceous matrix.

A strength test piece was prepared and subjected to a bending test. Theresult of the test is shown in Table 1. It can be seen from this thatthe bending strength had increased to twice the bending strength (4kg/mm²) of the commercial product I.

Furthermore, the thermal conductivity and the thermal expansivity wererespectively measured by the above-described methods. These results areshown in Table 1. The thermal conductivity had increased to 220 W/(m·K),which is more than twice that of the commercial product I (100 W/(m·K),and the thermal expansivity had risen from 3.8×10⁻⁶/° C. to 9.9×10⁻⁶/°C.

Example 3

Holes of a diameter of 10 mm and a depth of 100 mm were formed in ablock of commerically available artificial graphite I. After vacuumdegassing, it was heated in argon gas to 1550° C. for 210 minutes. Puremolten nickel heated to 1650° C. was then filled into the holes. Aplunger was then inserted therein whilst blowing the outer surface ofthe block with argon, and a pressure of 1000 kg per cm² of thecross-sectional area of the plunger was applied. This state wasmaintained for 30 minutes to impregnate the pores of the block ofartificial graphite I with nickel. After cooling, the portion of theblock impregnated with nickel was removed and cut to obtain acarbon-based nickel composite material having a nickel content of 12volume percent.

The nature of the nickel impregnation in the thus obtained carbon-basednickel composite material was observed, and the bending strength,thermal conductivity and thermal expansivity were respectively measured.The nature of the nickel impregnation was observed with the followingresults: no pores were observed and it could be confirmed that thenickel was dispersed uniformly in the carbonaceous matrix.

The bending strength had increased to 11 kg/mm², which is about threetimes the bending strength (4 kg/mm²) of the commerical artificialgraphite I; the thermal conductivity had increased from the 100 W/(m·K)of the commercial artificial graphite I to 170 W/(m·K), and the thermalexpansivity had become 7.5×10⁻⁶/° C. compared to the 3.8×10⁻⁶/° C. ofthe commcercial artificial graphite I.

These results are shown in Table 1.

Example 4

A block having a length (xy direction) of 100 mm, a width of 100 mm, anda depth (z direction) of 250 mm was prepared from a carbon fiber(pitch-type)-reinforced carbon composite material produced according toJapanese Patent Application Laid-Open Nos.247563/1991 and 157273/1996with stacks of fibers orientated at 0° and 90° (hereunder referred to as“2D carbon composite material” (refer to FIG. 2)).

Holes of a diameter of 10 mm and a depth of 100m were formed in theblock of 2D carbon composite material. After vacuum degassing, it washeated in argon gas to 1550° C. for 210 minutes. Pure molten nickelheated to 1650° C. was then filled into the holes, whilst cooling theouter surface of the block by blowing with argon gas. A pressure of 500kg per cm² of the cross-sectional area of the plunger was applied, andthis state was maintained for 30 minutes to impregnate the pores of theblock of 2D carbon composite material with nickel. After cooling, theportion of the block impregnated with nickel was removed and cut toobtain a carbon-based nickel composite material.

The nature of the nickel impregnation was observed; no pores could beobserved and it could be confirmed that the nickel was disperseduniformly in the carbonaceous matrix. The nickel content was 25 volumepercent.

A bending strength test piece was prepared and subjected to a bendingtest. The result is shown in Table 1. According to this result, thebending strength had increased 2.5 times in the xy plane from 20 kg/mm²prior to impregnation to 50 kg/mm², and had increased in the z planefrom less than 1 kg/mm² to 5 kg/mm².

The results of measuring the thermal conductivity are shown in Table 1.The thermal conductivity in the vertical direction with respect to thexy plane, i.e. in the z-axis direction had increased from 8 W/(m·K)prior to impregnation to 45 W/(m·K), and the thermal conductivity in thedirection of the x- or y-axis had increased from 200 W/(m·K) prior toimpregnation to 250 W/(m·K).

A nickel-impregnated test piece of 10 mm length and 3 mm in the verticaland horizontal directions was cut, and the surface thereof was coveredwith nickel to a total thickness of about 10 μm using electrolyticplating and non-electrolytic plating. This sample was placed in an airfurnace and left at 1000° C. for 1 hour. After cooling, it was removedand observed visually. There was no change other than that the nickelhad darkened. On the other hand, a sample of the non-impregnated 2Dcomposite material became reduced in mass to 38% of its original weight.

Comparative Example 1

A carbon-based aluminium composite having an aluminium content of 9.8volume percent was obtained in the same way as Example 1 except that themolten aluminium heated to 750° C. was added to the block of commercialartificial graphite I without preheating the block of commercialartificial graphite in argon gas. Observation of the nature of thealuminium impregnation showed that there were spaces in the open poreswhich had not been filled and that no more than 67 volume percent of thepores of the artificial graphite had been substituted with aluminium.The thermal conductivity was 133 W/(m·K) and the thermal expansivity was9.7×10⁻⁶/° C.; the thermal conductivity was insufficient. The results ofthe evaluation of the properties are shown in Table

Comparative Example 2

Aluminium impregnation was carried out in the same way as Example 1except that the pressure was 150 kg per cm² of the cross-sectional areaof the plunger. It was almost impossible to impregnate any aluminium,and a carbon-based aluminium composite material having satisfactoryproperties could not be obtained. The aluminium filling percentage was47 volume percent, and its content was 12%. The thermal conductivity was121 W/(m·K) and the thermal expansivity was 9.3×10⁻⁶/° C.

Comparative Example 3

An aluminium-impregnated carbon-based aluminium composite was preparedin the same way as Example 1 except that the composition was adjusted togive an aluminium content of 40 volume percent. The results of measuringthe bending strength, thermal conductivity and thermal expansivity areshown in Table 1. The aluminium filling percentage was favourable at100%, but the thermal expansivity was excessively high at 13.5×10⁻⁶/° C.giving a material of practically no use.

Comparative Example 4

An aluminium-impregnated carbon-based aluminium composite material wasobtained in the same way as Example 1 except that the pre-heatingtemperature was set to 600° C. which is below the melting point ofaluminium. The results of evaluating the properties are shown inTable 1. The aluminium filling percentage was low at 73 volume percentand there were problems with the thermal conductivity.

Comparative Example 5

A carbon-based aluminium composite material was prepared in the same wayas Example 1 except that a carbon formed body (average interplanarspacing {overscore (d)}₀₀₂=0.343 nm) obtained by calcinatingneedle-shaped coke, pitch and phenol resin for 3 hours at a finaltemperature of 2000° C. was used instead of artificial graphite. Theproperties are shown in Table 1.

This carbon formed body produced bubbles and broke up when soaked inwater.

Furthermore, when 30 nm cubes were left in air, they graduallypowderised and after about two weeks had completely lost their originalshape and become a powder body. It is supposed that this is caused bythe formation of aluminium carbide by a reaction between the carbon andaluminium.

TABLE 1 Metal Filling Bending Thermal Thermal Porosity PercentageStrength Conductivity Expansivity × (Vol. %) (Vol. %) kg/mm² W/(m.K)10⁻⁶/° C. Basic material: Commercial artificial graphite 12 0 4 100 3.8material I Example 1: Aluminium Impregnation 0 100 8 200 10.8 Example 2:Copper Impregnation 0 100 8 220 9.9 Example 3: Nickel Impregnation 0 10011 170 7.5 Comp. Example 1: Aluminium Impregnation 5 67 6 133 9.7 Comp.Example 2: Aluminium Impregnation 8 47 5 121 9.3 Comp. Example 3:Aluminium Impregnation 0 100 10 170 13.5 Comp. Example 4: AluminiumImpregnation 4 73 6 138 9.9 Parent material: Needle-shaped coke formedbody 25 0 2 70 1.8 Comp. Example 5: Aluminium Impregnation 0 100 6 1317.6 Parent Material: 2D Carbon Composite XY direction 20 200 0 25 0 2DCarbon Composite Z direction <1 8 7 Ex. 4: 2D Carbon Composite + NickelImpregnation 50 250 0 XY direction 0 100 2D Carbon composite + NickelImpregnation Z 5 50 10 direction Note: “2D Carbon Composite” refers to acomposite material produced by layer-stacking with the fibers directedin orthogonal directions; the xy direction is the fiber face, and the zdirection is the stacked layer face.

Example 5

A total of four types of carbon formed bodies, including 3 types ofcommercially available artificial graphite materials A, B and C, and onetype of carbon-fiber/carbon composite material were respectively heatedto 760° C. in argon gas for 90 minutes, and placed in molds heated to500° C. The molds were filled with pure aluminium melted at 810° C. Apress was used to apply a pressure of 500 kg per cm² of thecross-sectional area of the plunger, and this state was maintained for30 minutes. After cooling, the whole mass of aluminium was removed andcut to obtain a carbon-based aluminium composite material. The aluminiumfilling percentage ranged from 96 volume percent to 100 volume percent;and the content ranged from 7.7 volume percent to 27 volume percent.

The thermal conductivities, thermal expansivites and bending strengthsare shown in Table 2.

TABLE 2 Thermal Thermal Bending Metal Filling Density ConductivityExpansivity Strength Porosity percentage g/cm³ W/m.K. ×10⁻⁶/° C. kg/mm²Vol. % (Vol. %) Example 5 Artificial Graphite A Post-Impreg. 2.17 340 63 1 97 Pre-Impreg. 1.82 160 1 1 13 0 Artificial Graphite B Post-Impreg.2.26 200 7 5 0 100 Pre-Impreg. 1.53 100 3 2 27 0 Artificial Graphite CPost-Impreg. 2.17 190 8 10 0 100 Pre-Impreg. 1.85 100 4 5 12 0 Carbonfiber/carbon composite Post-Impreg. 2.14 450 11 — 0.3 96 Pre-Impreg.1.93 400 7 — 8 0 Comparative Example 6 Artiticial Graphite APost-Impreg. 2.07 250 5 2 4 70 Pre-Impreg. 1.82 160 1 1 13 0 Note:Artificial Graphite A: Maximum Particle Diameter 3 mm ArtificialGraphite B: Maximum Particle Diameter 0.8 mm Artificial Graphite C:Maximum Particle Diameter 0.1 mm Carbon fiber/carbon composite: thermalconductivity-value in fiber direction thermal expansivity-value indirection orthogonal to fiber direction

Comparative Example 6

A carbon-based aluminium composite material was obtained in the same wayas Example 5 except that the pure aluminium melted at 810° C. was addedwithout pre-heating the artificial graphite material A in the mold. Thealuminium filling percentage was 70 volume percent, and the aluminiumcontent was 9.1 volume percent. The thermal conductivity, thermalexpansivity and bending strength are shown in Table 2. The degree ofincrease in the thermal conductivity between prior to and afterimpregnation of this carbon-based composite material was low.

Example 6

Two types of carbon formed body, commercially available graphitematerials A and B, were used. Each carbon formed body was respectivelypre-heated to 960° C. in argon gas for 120 minutes, and then placed in amold heated to 600° C.

The mold was then filled with 7-3 brass melted at 960° C. A pressure of1000 kg per cm² of the cross-sectional area of the plunger was applied,and this state was maintained for 30 minutes to impregnate the carbonformed body with the 7-3 brass and form the composite. After cooling,the whole mass of 7-3 brass was removed and cut to obtain a carbon-based7-3 brass composite material.

The 7-3 brass filling percentage was 94 volume percent and the 7-3 brasscontent was 12 volume percent and 25 volume percent.

The results of measuring the thermal conductivity, thermal expansivityand bending strength are shown in Table 3.

TABLE 3 Thermal Thermal Bending Metal Filling Density ConductivityExpansivity Strength Porosity percentage g/cm³ W/(m.K.) ×10⁻⁶/° C.kg/mm² Vol. % (Vol. %) Artificial Graphite A Post-Impreg. 2.91 200 5 20.8 95 Pre-Impreg. 1.82 160 1 1 13 0 Artificial Graphite B Post-Impreg.3.75 190 6 3 1.6 95 Pre-Impreg. 1.53 100 3 2 27 0 Note: Artificialgraphite material A: max. particle diameter 3 mm Artificial graphitematerial B: max. particle diameter 0.8 mm

The following points were clear from the results of Examples 5 and 6.The thermal conductivity had risen by up to 100 W/(m·K) compared to thecarbon formed body prior to impregnation, making it possible to achievea thermal conductivity of 200 W/(m·K) or greater which is demanded forthe base substrate of an electronic component. Furthermore, it is shownthat the thermal expansivity could be freely controlled from 5×10⁻⁶/° C.to 11×10⁻⁶/° C. by selecting the type of metal or type of carbon formedbody. This thermal expansivity is similar to that of silicon (3×10⁻⁶/°C. to 4×10⁻⁶/° C.), and that of aluminium nitride (4.5×10⁻⁶/° C.) oralumina (7×10⁻⁶/° C.), which are each mounted on the substrate.Accordingly, a substrate employing the carbon-based metal compositematerial of the present invention can reduce the amount of thermalstress produced by differences in thermal expansivity between thesubstrate and electronic components mounted thereon, making it possibleto inhibit the generation of defects such as warping and peeling.

Example 7

Commercially available artificial graphite was cut to prepare two carbonformed bodies of length 100 mm, width 100 mm and depth 10 mm for use assubstrates. A semicircular-shaped groove of diameter 12 mm was cut intothe substrates; a stainless steel pipe of external size 9.5 mm andpreformed to match the grooves was sandwiched and provisionally fixedbetween the two substrates. This was then placed in a metal mold andpre-heated to 750° C. in argon gas for 90 minutes. Aluminium (JISAC4CH)melt was poured in and cast at a pressure of 500 kg/cm². After cooling,it was cut to obtain the substrate-shaped carbon formed body for anelectronic component shown in FIG. 4. The aluminium filling percentageof the formed body was 99 volume percent and the aluminium content was12 volume percent; the thermal conductivity and thermal expansivity were200 W/(m·K) and 5×10⁻⁶/° C., respectively.

Example 8

A substrate produced by subjecting a carbon composite body having carbonfibers orientated in a single direction to cutting orthogonally to thefiber direction was used to provide a carbon formed body of length 50mm, width 50 mm and depth 10 mm. 20 grooves of length 50 mm, width 1 mmand depth 2 mm were cut into the carbon formed body at a pitch of 2 mm.Thin plates of length 50 mm, width 20 mm and depth 0.9 mm and cut fromartificial graphite material were inserted into the grooves. This wasthen provisionally fitted via a mold-release agent in a mold made fromsteel material. This was then placed in a mold and pre-heated to 750° C.in argon gas. Aluminium (JISSAC4CH) melt was poured in and cast at apressure of 500 kg/cm². After cooling, it was removed from the mold andcut (refer to FIG. 5-1 and FIG. 5-2). The aluminium filling percentagewas 99 volume percent and the aluminium content was 9 volume percent;the thermal conductivity and the thermal expansivity were 400 W/(m·K)and 10×10⁻⁶/° C., respectively.

Comparative Example 7

A carbon formed body indentical to the carbon formed body of Example 7was prepared as a substrate, and a substrate-shaped carbon formed bodyfor an electronic component comprising a carbon-based aluminiumcomposite material was obtained in the same way as Example 7 except thatthe aluminium impregnation was carried out without pre-heating thecarbon formed body. The aluminium filling percentage was 40 volumepercent, the aluminium content was 5 volume percent, the thermalconductivity was 124 W/(m·K) and the thermal expansivity was 6×10⁻⁶/° C.

In Example 7, observation of a cut face of the carbon formed body with amicroscope revealed that the aluminium had completely filled the spacesin the carbon formed body. Furthermore, the gap between the stainlesssteel pipe and the substrates was filled with aluminium without anyspaces thereby achieving integration. In Comparative Example 7, thefilling of the spaces of the carbon formed body was not complete, andthe integration was not sufficient. The thermal expansivity of thesubstrates of Examples 7 and 8 was close to that of silicon, alumina andaluminium nitride. Furthermore, there were no spaces at the interfacejoining the substrates and the cooling pipe or fins resulting inexcellent thermal conductivity.

Example 9

A carbon-based copper composite material produced by impregnating aunidirectionally orientated carbon-fiber carbon composite having aporosity of 8% with molten copper at high pressure according to themethod of Example 1 was used to prepare a 30 mm substrate piece having athickness of 3 mm (thickness direction is longitudinal direction offibers). The copper filling percentage was 93 volume percent, the coppercontent was 7.4 volume percent, and the density was 2.6 g/cm³. A metalfilm mainly comprising molybdenum and chromium and having a thickness of10 microns was formed on the substrate by plasma spraying. White aluminahaving a purity of 99.6% and an average particle diameter of 1 μm wasplasma sprayed onto this metal film to prepare a ceramics film with atotal film thickness of 0.1 mm with the metal coating. Since pinholeswere present in this film, a glass flit was thinly laid on the film andcalcined at 900° C. An aluminium foil of thickness 10 μm was laid onthis film, and then a copper foil of thickness 0.3 μm was stacked on topthereof. It was then treated using a hot press for 30 minutes at 2MPaand 650° C. to obtain a copper plated substrate. An example of the usein an electronic component of a carbon-based metal composite materialprovided with an insulating film is shown in FIG. 6. In the figure, aceramics insulating film 62 is provided on a substrate (60) employingthe carbon-based metal composite material via a joining layer (61) ofsolder. An electronic circuit (63) and electronic parts (64) aredirectly provided on top of this film.

In order to confirm the electrical insulating properties of the ceramicsfilm, a potential difference of 500V was applied between thecarbon-based metal composite material substrate and the copper plate andthe electrical resistance was measured using an electrical insulationtester. The electrical resistance was infinitely large therebyconfirming the electrical insulating properties of the ceramics film.

Example 10

The surface of a 10 mm carbon-based copper composite material substratesimilar to that of Example 9 and having a thickness of 1 mm was polishedto give an average surface roughness of 0.1 μm. A magnetron sputteringdevice was used to form an alumina film of 0.03 mm on the substrate byflowing 10 ml per minute of a gas mixture consisting of 9 parts argongas and I part oxygen gas at an atmosphere pressure of 1 Pa for 12 hoursat a power output of 300 W. The temperature of the substrate at thistime was 300° C.

The alumina substrate film was observed with a scanning electronmicroscope at a magnification ratio of ×5000. The film was transparentand glassy. No defects such as pinholes, and cracks were observed.

In order to confirm the heat resistance of this substrate, the step ofheating the substrate in air to 400° C. and then allowing it to coolnaturally was repeated 5 times, and then the substrate was observed witha scanning electron microscope at a magnification ratio of ×5000. Nodefects such as cracks or pinholes were observed proving that thesubstrate is heat-resistant at a temperature of 400° C. Metal was thendeposited on the alumina film applied using the magnetron sputteringdevice, and the dielectric strength of the film was measured by testingthe electrical insulating properties of the metal film and carbon-basedcopper composite material using an electrical insulator tester. Thedielectric strength of the film was between 500V and 650V. Furthermore,the specific resistivity of the film was measured to be at least10¹²Ω-m.

Comparative Example 8

A carbon-based copper composite material provided with a ceramics filmwas prepared in the same way as Example 10 except that a carbon formedbody substrate having a copper filling percentage of 95 volume percent,a copper content of 45 volume percent and a thermal expansivity of12.5×10⁻⁶/° C. was used. When the substrate was heated to 250° C. andallowed to cool naturally to room temperature, cracks were observed inthe ceramics film as a result of the difference in thermal expansivitybetween the carbon-based copper composite material and the ceramicsfilm.

INDUSTRIAL APPLICABILITY

The carbon-based metal composite material of the present invention hasat least 90 volume percent of the pores of the carbonaceous matrixsubstituted with a metal component, and has a metal component content of35 volume percent or less. Its high thermal conductivity and low thermalexpansivity make it useful as a heat disperser for an electroniccomponent. It can also be used as a structural material forastronautical components or a general structural material havingexcellent specific strength and specific rigidity, and an extremelygreat industrial contribution has thus been made by the provision ofthis novel material.

Furthermore, the method of producing a carbon-based metal compositematerial according to the present invention is also useful as means forproviding said composite material, and it is likewise of greatindustrial use in that it solves the problems associated with moltenmetal, particularly, aluminium impregnation which was considered asimpossible in the prior art.

What is claimed is:
 1. A carbon-based metal composite materialcomprising a carbonaceous matrix and a metal component dispersed in saidcarbonaceous matrix, characterized in that (1) the carbonaceous matrixis a pressure formed body comprising at least one type of carbonmaterial selected from the group consisting of graphite crystallinecarbon materials, carbon powder and artificial graphite powder; (2) atleast 90 volume percent of the pores of the carbonaceous matrix issubstituted with a metal component; and (3) the content of said metalcomponent is 35% or less based on the total volume of said carbon-basedmetal composite material.
 2. The carbon-based metal composite materialaccording to claim 1 wherein the metal component is at least one metalselected from the group consisting of aluminmum, magnesium, tin, zinc,copper, silver, nickel and alloys thereof.
 3. The carbon-based metalcomposite material according to claim 2 wherein said metal component isat least one pure metal component selected from the group consisting ofalununium, copper and silver.
 4. The carbon-based metal compositematerial according to claim 1 wherein the average interplanar spacing{overscore (d)}₀₀₂ of the graphite crystals of said graphite crystallinecarbon material is 0.340 nm or less.
 5. The carbon-based metal compositematerial according to claim 1 wherein at least 95 volume percent of thepores of said carbonaceous matrix is substituted with said metalcomponent.
 6. The carbon-based metal composite material according to anyone of claims 1 to 3, wherein the content of said metal component is 5%to 30% based on the total volume of said carbon-based metal compositematerial.
 7. A method of producing a carbon-based metal compositematerial comprising impregnating a carbon formed body with a moltenmetal by contacting said carbon formed body with said molten metal underpressure, characterized by (1) pre-heating said carbon formed body in aninert atmosphere to a temperature at least as high as the melting pointof said molten metal, and (2) impregnating the pre-heated carbon formedbody with said molten metal at a pressure of at least 200 kg per cm² ofthe plunger cross-sectional area wherein said carbon formed body is agraphite crystalline carbon material calcinated at a temperature of atleast 2500° C. and having an average interplanar spacing d₀₀₂ of 0.340nm or less.
 8. The method of producing a carbon-based metal compositematerial according to claim 7 wherein said carbon formed body has aporosity of 5 volume percent to 30 volume percent.
 9. The method ofproducing a carbon-based metal composite material according to claim 7wherein said pre-heating temperature is at least 100° C. higher than themelting point of said molten metal.
 10. The method of producing acarbon-based metal composite material according to claim 7 wherein saidimpregnation temperature is 50° C. to 250° C. higher than the meltingpoint of said molten metal.
 11. A carbon, based metal composite materialfor an electronic component characterized in that it is formed from acarbon-based metal composite material having a density of 2.0 g/ml to2.5 g/ml, a thermal conductivity of at least 150 W/m·K and a thermalexpansivity of 4×10⁻⁶/° C. to 8×10⁻⁶/° C., which comprises acarbonaceous matrix and aluminum or aluminum alloy dispersed in saidcarbonaceous matrix, characterized in that (1) the carbonaceous matrixis a pressure formed body comprising at least one type of carbonmaterial selected from the group consisting of graphite crystallinecarbon materials, carbon powder and artificial graphite powder; (2) atleast 90 volume percent of the pores of the carbonaceous matrix issubstituted with a metal component; and (3) the content of said metalcomponent is 35% or less based on the total volume of said carbon-basedmetal composite material.
 12. The substrate-shaped formed body for anelectronic component according to claim 11 wherein said substrate-shapedformed body has a thickness of 0.1 mm to 20 mm.
 13. The substrate-shapedformed body for an electronic component according to claim 11, whereinsaid carbon formed body is a cooling device-fitted substrate obtained byintegration via metal with a cooling device having a liquid as thecooling medium.
 14. A carbon-based metal composite material providedwith an insulating film obtained by covering the surface of acarbon-based metal composite material according to claim 1 or acarbon-based metal composite material obtained by a method according toclaim 8 with an insulating material.
 15. The carbon-based metalcomposite material provided with an insulating film according to claim14 wherein said insulating material is a plastic or ceramics material.16. The carbon-based metal composite material provided with aninsulating film according to claim 14 wherein the thickness of saidcovering layer of insulating material is 0.6 mm or less.
 17. A carbonbased metal composite material for an electronic component characterizedin that it is formed from a carbon-based metal composite material,having a density of 2.3 g/ml to 4.6 g/ml, a thermal conductivity of atleast 150 W/m·K) and a thermal expansivity of 4×10⁻⁶/° C. to 12×10⁻⁶/°C., which comprises a carbonaceous matrix and copper, silver or an alloythereof dispersed in said carbonaceous matrix, characterized in that (1)the carbonaceous matrix is a pressure formed body comprising at leastone type of carbon material selected from the group consisting ofgraphite crystalline carbon materials, carbon powder and artificialgraphite powder; (2) at least 90 volume percent of the pores of thecarbonaceous matrix is substituted with a metal component; and (3) thecontent of said metal component is 35% or less based on the total volumeof said carbon-based metal composite material.